This invention relates to a ball-type chucking mandrel that is used for the self-centering of valve stems of gas-changing valves as they are used in internal-combustion engines.
At a certain axial distance, two ball-type chucking mandrels are arranged mirror-symmetrically to one another. The advantage of the ball-type chucking mandrels is that with the precise centering characteristics of the chucking mandrel, larger diameter tolerances of the workpiece to be received may also be permitted. Since balls can be made with high precision in regard to shape and with a low diametrical tolerance, high centering precision can be achieved by means of ball-type chucking mandrels. A disadvantage of the ball-type chucking mandrels is that because of the point contact only relatively low chucking powers can be applied. It is also a disadvantage in the case of the known ball-type chucking mandrels that only small torques can be transferred since, despite a certain bracing of the chucking balls between the conical surfaces and the workpiece, a "ball bearing effect" will still occur. A rolling-off of the balls occurs between the workpiece to be braced and the conical surface. It is true that the known ball-type chucking mandrel has a guide cage for the chucking balls which is fixed in the rotating direction and thus hinders this rolling process. Nonetheless, a certain rolling-off effect can still occur, namely when the chucking balls can turn within the cage.
It is an objective of the invention to improve the ball-type chucking mandrels on which this invention is based, without a cage for the chucking balls, in such a way that the "ball bearing effect" that occurs can be avoided and larger torques may be transferred by means of the ball-type chucking mandrels.
This objective is achieved by rigidly connecting the balls together in pairs. Because of the pairing of two chucking balls into a rigid dumbbell-shaped unit, a rolling-off of the balls in the circumferential direction is avoided. In addition, because of this arrangement and the mutual connection of the chucking balls, their number is increased, which also increases the chucking power. The centering precision is not affected by the precision of the mutual fixing of two balls into a pair of balls. In the case of a rod-shaped connection of two balls by means of a connecting pin, this connecting pin may easily extend eccentrically with respect to the center of the ball. The mutual distance of the balls within the pair of balls is also not critical.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings(s) which show, for purposes of illustration only, an embodiment/several embodiments in accordance with the present invention.